1. Field of the Invention
The invention relates to a method for producing organosilicon compounds having carbonyl radicals, and the use thereof.
2. Description of the Related Art
Aldehydes and ketones are widely used in organic chemistry and are important precursors in the synthesis of, for example, heterocycles, fragrances and dyes. In organosilicon chemistry, on the other hand, aldehyde and ketone functions play only a minor role in spite of their extremely interesting reaction profile. The reason for this is the lack of a suitable synthesis route which permits the production of organosilicon compounds having carbonyl radicals in a simple and rapid manner and with high yields.
Only three methods for preparing siloxanes having aldehyde and ketone functionalities are known to date:
FR 1,531,637 A describes the platinum-catalyzed addition reaction of olefins having a blocked aldehyde or ketone function, such as, for example, 1-trimethylsilyloxy-1,3-butadiene, 2-trimethylsilyloxy-4-methyl-1,3-butadiene or 4-trimethylsilyloxy-2-methyl-1,3-butadiene, with hydrido-functional organosilicon compounds and the subsequent hydrolysis step for liberating the carbonyl function. In comparison, FR 1,224,081 A and U.S. Pat. No. 2,803,637 A claim the hydrosilylation of aliphatically unsaturated aldehyde acetals with subsequent, acidic acetal cleavage. Starting materials suitable for this purpose are, for example, acrolein dimethyl acetal, acrolein diethyl acetal, methacrolein diacetate, undecenyl diethyl acetal, octadecenyl diethyl acetal, ketene diethyl acetal, 3-cyclohexene-1-carboxaldehyde diethyl acetal, 5-norbornene-2-carboxaldehyde diethyl acetal or bicyclo[2.2.2]oct-5-ene-2-carboxaldehyde diethyl acetal. Common to the processes is that the desired products are obtainable via a plurality of stages only in moderate yield, in particular the hydrolysis step being tedious and generally extremely problematic owing to the heterogeneous system. In addition, the number of aldehyde or ketone substituents obtainable on an industrial scale in this way is greatly limited by the limited commercial availability of suitable acetals.
According to EP 392 948 A1, EP 402 274 A1 and U.S. Pat. No. 5,021,601 A, polyorganosiloxanes having 1-formylethyl or 2-formylethyl groups are obtainable by hydroformylation of the corresponding vinyl-functional organosilicon compounds. The polysiloxanes which are used as intermediates in DE 36 32 869 A1 and contain tricyclo[5.2.1.02,6] decadiene derivative groups substituted by formyl groups are obtained by basically the same process. A disadvantage of the hydroformylation process is that the conversion of the olefin group takes place only at high pressure and high temperature, and furthermore a quantitative conversion is to be realized only by a very complex procedure. Usually, such sytheses are therefore carried out in an autoclave at a superatmospheric pressure of from 20 to 200 bar and a temperature of 100-150° C. which requires special apparatuses and knowledge about handling the gaseous reactants CO and H2. Moreover, here too the number of aldehyde or ketone substituents obtainable by this method is limited.
U.S. Pat. No. 2,947,770 A and U.S. Pat. No. 5,739,246 A describe a method for preparing carbonyl-functional siloxanes via the ozonolysis of alkenyl-functionalized organosilicon compounds and subsequent reductive cleavage of the ozonide formed. A particular disadvantage of this method is that the ozonolysis of double bonds leads to the degradation of the unsaturated carbon skeleton and hence to a loss of at least one carbon unit.
Furthermore, a large number of by-products formed in the ozonolysis, the costs for producing or handling ozone and the stipulation of a few suitable starting compounds prevent the wide use of this method on the industrial scale.